The present invention relates to drive shafts or propeller shafts which are designed to suppress whirling vibrations, and more specifically to two-piece type (or three-joint type) drive shafts for transmitting power from an engine or motor of a vehicle toward driving wheels in such a manner as to reduce undesired vibrations and noises.
FIG. 6 shows one conventional drive shaft assembly for a motor vehicle. Various drive shaft assemblies are shown in "Shinpen Jidosha Kogaku Binran" (June, 1987; Society of Automotive Engineers of Japan), vol. 5, chapter 1, part 4 (pages 25.about.29). The drive shaft assembly shown in FIG. 6 is a three-joint type assembly, and includes first and second shaft tubes 12 and 13, and three universal joints 14, 15 and 16, such as Cardan joints. Both shaft tubes 12 and 13 are connected end to end by the middle joint 16. A center bearing 17 is provided to support an intermediate portion of said first shaft tubes 12 to a vehicle body.
The drive shaft is a long part rotating at high speeds. Therefore, the drive shaft lacking rotating balance causes serious vibration and noise problems. The shaft unbalance is usually corrected by measuring an amount of unbalance with a dynamic balance test equipment, and attaching a balance weight to the shaft at a proper position. However, it is practically impossible to make a completely balanced shaft whose axis of inertia is coincident with the center axis of the shaft.